As a technique for supporting mobility in an IP network, Mobile IPv6 (MIP) has been proposed by IETF (Internet Engineering Task Force) (see Non-Patent Document 1). MIP allows a communication to continue even if a mobile terminal device moves by placing a mobility control node called Home Agent in a network and managing a position of the mobile terminal device in this node. As a technique for improving performance of handover (hereinafter abbreviated as HO), Hierarchical Mobile IPv6 (HMIP) has been proposed (see Non-Patent Document 2). In HMIP, a Mobility Anchor Point (hereinafter abbreviated as MAP) is newly defined as a mobility control node in a network and a position of a mobile terminal device in a local area is managed, so that disruption time by HO is reduced.
FIG. 9 is a diagram which shows an operation example of HMIP. In the figure, according to HMIP, MAP information of a network in which a mobile terminal device is currently located is managed in a Home Agent (hereinafter abbreviated as HA) 40. An MAP 30 manages a mobile terminal identifier assigned by an access router (hereinafter abbreviated as AR) to which a mobile terminal device 10 currently connects. Thereby, a packet sent from a communication partner (Correspondent Node; hereinafter abbreviated as CN) 50 is passed sequentially through the HA 40, the MAP 30, and the AR 21 to which the mobile device connects and finally forwarded to the mobile terminal device.
In HMIP, the mobile terminal device 10 has acquired information of the MAP 30 in advance, and, if an HO from the AR 21 to an AR 22 is performed (step S51), then a mobile terminal identifier assigned by the currently connected AR 22 is notified to the MAP 30 (step S52). Route switching is thereby performed (step S53). From then on, when the MAP 30 receives a packet from the CN 50, the MAP 30 can transfer the packet to the mobile terminal device also after HO by forwarding the packet to the AR 22.    Non-Patent Document 1: D. Johnson, et al., “Mobility Support in IPv6,” RFC3775, June 2004    Non-Patent Document 2: H. Soliman, et al, “Hierarchical Mobile IPv6 mobility management (HMIPv6),” draft-ietf-mipshop-hmipv6-04.txt, December 2004
In the above described HMIP, HO whose delay is shorter than in MIP is achieved by introducing an MAP. However, in HMIP, since route switching is performed by a mobile terminal device, the mobile terminal device has to recognize an address of an MAP. In addition, a signaling function for registering a position with an MAP is added to the function of MIP. Therefore, a mobile terminal device which has no function of HMIP cannot enjoy the effect of delay time reduction due to placing an MAP.
Thus, because HMIP is a scheme which expands the function of MIP, it is not only required that an MAP is added to a network, but also that a function is added to a mobile terminal device in such a manner that the mobile terminal device recognizes an address of the MAP, signaling is performed between the MAP and the mobile terminal device or the like. Therefore, a mobile terminal device which supports only MIP cannot perform the function of HMIP in a network where HMIP has been deployed.
Additionally, in HMIP, while movement is performed within a local network formed by an MAP, the same MAP is continually used. Therefore, it is concerned that a route becomes redundant if a mobile terminal device moves while continuing communication. To solve this, a technique for changing an MAP is also being examined. However, since this requires complicated control, the problem of reduction of HO processing capacity is caused by increase of the number of control message transmitted within wireless and wired zones and delay time associated with complexity of the control.
The present invention is made to solve the problems of the prior arts described above, and intended to provide an access router device, a mobility control system, and a mobility control method which can achieve movement between local networks formed by mobility control nodes without adding a function to the mobile terminal device.